S.Korea's president asks rival to be PM-source

SEOUL, June 11 (Reuters) - South Korea's unpopular president has informally asked his main conservative rival to be his prime minister to stem a wave of discontent over his policies that has triggered mass street protests, an aide to the rival said on Wednesday.

President Lee Myung-bak, whose support rate has plunged to below 20 percent after just 100 days in office, has made an unofficial request to Park Geun-hye to join his government as the premier, the aide to Park told Reuters.

"There is a chance she could accept if a formal request is made because the situation is so difficult," said the aide, who asked not to be named.

Park, who once ran the conservative Grand National Party and is the daughter of an assassinated dictator, is seen as being able to unite the faction-ridden party and bring a steadying hand to Lee's government, roundly criticised for bungling a deal to import U.S. beef and being out of touch with public sentiment. (Reporting by Lee Suwan; Writing by Jon Herskovitz; Editing by Keiron Henderson and Alex Richardson)